Properly set cmsg_len in CMSG_NXTHDR tests.

gibbz00 · tgross35 · commit f391df35f33a · 2026-01-04T23:38:37.000Z
Setting `(*pcmsghdr).cmsg_len = cmsg_len as _;` when cmsg_len ranges
from 0 to 64 is invalid as it must always be `&gt;= size_of::&lt;cmsghdr&gt;()`,
rounded up to the nearest alignment boundary.

Some implementations (notably glbic) do check that `cmsg_len &gt;=
size_of::&lt;cmsghdr&gt;()` in `CMSG_NXTHDR`, returning null if so. But
this is more so an extra precaution that is not mentioned in the POSIX
1003.1-2024. It can therefore not be relied on for tests executed on
multiple platforms.

The change also removes the ignoring of some testvalues when targeting AIX.
diff --git a/libc-test/tests/cmsg.rs b/libc-test/tests/cmsg.rs
@@ -74,14 +74,10 @@ mod t {
             let pcmsghdr = buffer.0.as_mut_ptr().cast::<cmsghdr>();
             mhdr.msg_control = pcmsghdr.cast::<c_void>();
             mhdr.msg_controllen = (160 - start_ofs) as _;
-            for cmsg_len in 0..64 {
-                // Address must be a multiple of 0x4 for testing on AIX.
-                if cfg!(target_os = "aix") && cmsg_len % std::mem::size_of::<cmsghdr>() != 0 {
-                    continue;
-                }
+            for cmsg_payload_len in 0..64 {
                 unsafe {
                     pcmsghdr.cast::<u8>().write_bytes(0, CAPACITY);
-                    (*pcmsghdr).cmsg_len = cmsg_len as _;
+                    (*pcmsghdr).cmsg_len = libc::CMSG_LEN(cmsg_payload_len as _) as _;
                     let libc_next = libc::CMSG_NXTHDR(&mhdr, pcmsghdr);
                     let next = cmsg_nxthdr(&mhdr, pcmsghdr);
                     assert_eq!(libc_next, next);
